JDK14/Java14源码在线阅读

/*
 * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
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 */

package sun.jvm.hotspot.oops;

import java.io.*;
import java.util.*;

import sun.jvm.hotspot.debugger.*;
import sun.jvm.hotspot.runtime.*;
import sun.jvm.hotspot.types.*;
import sun.jvm.hotspot.utilities.*;

public class Mark extends VMObject {
  static {
    VM.registerVMInitializedObserver(new Observer() {
        public void update(Observable o, Object data) {
          initialize(VM.getVM().getTypeDataBase());
        }
      });
  }

  private static synchronized void initialize(TypeDataBase db) throws WrongTypeException {
    Type type  = db.lookupType("oopDesc");
    markField  = type.getCIntegerField("_mark");

    ageBits             = db.lookupLongConstant("markWord::age_bits").longValue();
    lockBits            = db.lookupLongConstant("markWord::lock_bits").longValue();
    biasedLockBits      = db.lookupLongConstant("markWord::biased_lock_bits").longValue();
    maxHashBits         = db.lookupLongConstant("markWord::max_hash_bits").longValue();
    hashBits            = db.lookupLongConstant("markWord::hash_bits").longValue();
    lockShift           = db.lookupLongConstant("markWord::lock_shift").longValue();
    biasedLockShift     = db.lookupLongConstant("markWord::biased_lock_shift").longValue();
    ageShift            = db.lookupLongConstant("markWord::age_shift").longValue();
    hashShift           = db.lookupLongConstant("markWord::hash_shift").longValue();
    lockMask            = db.lookupLongConstant("markWord::lock_mask").longValue();
    lockMaskInPlace     = db.lookupLongConstant("markWord::lock_mask_in_place").longValue();
    biasedLockMask      = db.lookupLongConstant("markWord::biased_lock_mask").longValue();
    biasedLockMaskInPlace  = db.lookupLongConstant("markWord::biased_lock_mask_in_place").longValue();
    biasedLockBitInPlace  = db.lookupLongConstant("markWord::biased_lock_bit_in_place").longValue();
    ageMask             = db.lookupLongConstant("markWord::age_mask").longValue();
    ageMaskInPlace      = db.lookupLongConstant("markWord::age_mask_in_place").longValue();
    hashMask            = db.lookupLongConstant("markWord::hash_mask").longValue();
    hashMaskInPlace     = db.lookupLongConstant("markWord::hash_mask_in_place").longValue();
    biasedLockAlignment  = db.lookupLongConstant("markWord::biased_lock_alignment").longValue();
    lockedValue         = db.lookupLongConstant("markWord::locked_value").longValue();
    unlockedValue       = db.lookupLongConstant("markWord::unlocked_value").longValue();
    monitorValue        = db.lookupLongConstant("markWord::monitor_value").longValue();
    markedValue         = db.lookupLongConstant("markWord::marked_value").longValue();
    biasedLockPattern = db.lookupLongConstant("markWord::biased_lock_pattern").longValue();
    noHash              = db.lookupLongConstant("markWord::no_hash").longValue();
    noHashInPlace       = db.lookupLongConstant("markWord::no_hash_in_place").longValue();
    noLockInPlace       = db.lookupLongConstant("markWord::no_lock_in_place").longValue();
    maxAge              = db.lookupLongConstant("markWord::max_age").longValue();
  }

  // Field accessors
  private static CIntegerField markField;

  // Constants -- read from VM
  private static long ageBits;
  private static long lockBits;
  private static long biasedLockBits;
  private static long maxHashBits;
  private static long hashBits;

  private static long lockShift;
  private static long biasedLockShift;
  private static long ageShift;
  private static long hashShift;

  private static long lockMask;
  private static long lockMaskInPlace;
  private static long biasedLockMask;
  private static long biasedLockMaskInPlace;
  private static long biasedLockBitInPlace;
  private static long ageMask;
  private static long ageMaskInPlace;
  private static long hashMask;
  private static long hashMaskInPlace;
  private static long biasedLockAlignment;

  private static long lockedValue;
  private static long unlockedValue;
  private static long monitorValue;
  private static long markedValue;
  private static long biasedLockPattern;

  private static long noHash;

  private static long noHashInPlace;
  private static long noLockInPlace;

  private static long maxAge;

  /* Constants in markWord used by CMS. */
  private static long cmsShift;
  private static long cmsMask;
  private static long sizeShift;

  public Mark(Address addr) {
    super(addr);
  }

  public long value() {
    return markField.getValue(addr);
  }

  public Address valueAsAddress() {
    return addr.getAddressAt(markField.getOffset());
  }

  // Biased locking accessors
  // These must be checked by all code which calls into the
  // ObjectSynchoronizer and other code. The biasing is not understood
  // by the lower-level CAS-based locking code, although the runtime
  // fixes up biased locks to be compatible with it when a bias is
  // revoked.
  public boolean hasBiasPattern() {
    return (Bits.maskBitsLong(value(), biasedLockMaskInPlace) == biasedLockPattern);
  }

  public JavaThread biasedLocker() {
    Threads threads = VM.getVM().getThreads();
    Address addr = valueAsAddress().andWithMask(~(biasedLockMaskInPlace & ageMaskInPlace));
    return threads.createJavaThreadWrapper(addr);
  }

  // Indicates that the mark gas the bias bit set but that it has not
  // yet been biased toward a particular thread
  public boolean isBiasedAnonymously() {
    return hasBiasPattern() && (biasedLocker() == null);
  }

  // lock accessors (note that these assume lock_shift == 0)
  public boolean isLocked() {
    return (Bits.maskBitsLong(value(), lockMaskInPlace) != unlockedValue);
  }
  public boolean isUnlocked() {
    return (Bits.maskBitsLong(value(), biasedLockMaskInPlace) == unlockedValue);
  }
  public boolean isMarked() {
    return (Bits.maskBitsLong(value(), lockMaskInPlace) == markedValue);
  }

  // Special temporary state of the markWord while being inflated.
  // Code that looks at mark outside a lock need to take this into account.
  public boolean isBeingInflated() {
    return (value() == 0);
  }

  // Should this header be preserved during GC?
  public boolean mustBePreserved() {
     return (!isUnlocked() || !hasNoHash());
  }

  // WARNING: The following routines are used EXCLUSIVELY by
  // synchronization functions. They are not really gc safe.
  // They must get updated if markWord layout get changed.

  public boolean hasLocker() {
    return ((value() & lockMaskInPlace) == lockedValue);
  }
  public BasicLock locker() {
    if (Assert.ASSERTS_ENABLED) {
      Assert.that(hasLocker(), "check");
    }
    return new BasicLock(valueAsAddress());
  }
  public boolean hasMonitor() {
    return ((value() & monitorValue) != 0);
  }
  public ObjectMonitor monitor() {
    if (Assert.ASSERTS_ENABLED) {
      Assert.that(hasMonitor(), "check");
    }
    // Use xor instead of &~ to provide one extra tag-bit check.
    Address monAddr = valueAsAddress().xorWithMask(monitorValue);
    return new ObjectMonitor(monAddr);
  }
  public boolean hasDisplacedMarkHelper() {
    return ((value() & unlockedValue) == 0);
  }
  public Mark displacedMarkHelper() {
    if (Assert.ASSERTS_ENABLED) {
      Assert.that(hasDisplacedMarkHelper(), "check");
    }
    Address addr = valueAsAddress().andWithMask(~monitorValue);
    return new Mark(addr.getAddressAt(0));
  }

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